The Camelback is probably my favorite resort in the Marriott system. The location is great, the private "casitas" are great, the property is great and the restaurants are great.
Weather wise, you should be in luck during May. The furnice won't be maxing out yet so it should be comfortable. My last trip to this resort was during the month of August and my skin was on the verge of blistering off even when I was hanging out in the shade.